Stands for "too long, didn't read". It can be interpreted in different ways depending on the context.

1. When responding as a first post, and only as a first post, on a thread, it means the OP's post was so long and unimportant or uninteresting that the user deemed it unworthy of his/her time. If the topic really is unimportant and uninteresting, and long enough to need more than a minute to be read and understood, the user ends up looking clever, though on some communities the user may end up looking like a troll or a lazy bum.

2. When responding during an already ongoing discussion where others haven't used the term, it means the user is trying to diminish the topic's importance or entertainment value, but considering that such a strategy won't work in a discussion where people are actually participating, the user ends up looking like a dipshit.

3. When responding with it during an argument, it means that the user in question wants to win the argument by stating that what the other person is saying is so worthless it's not worth reading. But by evading the argument instead of confronting it directly, it becomes obvious that the user got owned.

1.

- someguy1: *posts a very large and boring flow chart about people in facebook*
- User: tl;dr
- others: I second that.

*on a community where users actually like these things*
- User: tl;dr
- others: If you think it's too long then GTFO, retard.

2.

- User: tl;dr
*some ignore dipshit and continue discussion, some others tell the dipshit to GTFO, everyone will report the post to mods*

"too long; didn't read."
1. The inability to accept, understand or pay attention to information when not separated by a header.
2. The ability to arbitrarily read 400 small posts but not a long one.
3. A sign of ADD or lack of reading capability.
4. A very cheap response and an indication of lack of wit.
5. 90% of the time: A lie.
6. A desperate attempt at a comeback used by people who just can't think of one.
7. Usually used by people who've been torn apart verbally but want one last attempt at looking witty.
8. Total failure at #7.
7. A sign that, not only is someone too lazy and stupid to read but, clearly, too lazy and stupid to even type out four words indicating such.
9. Collect every "tl,dr" post online, and you'll have a good estimate of the number of lazy idiots on Earth, who currently have Internet access.
10. Should really be:
"Too Lazy, Don't Read."
or,
".....I got nut'n!"

~ ME:
.....Therefore you suck fabulous donkey shit cock.
~ "Smart Troll" Not Used To Being Beaten:
*yawn* tl;dr
~ Me:
...Right, well, as believable as that is, you've got time. Just sound the bigger words out. Now I can see why your friends say you're so "smart".

"Too Long; Didn't Read" - a shining example of the sweeping Attention Deficit Disorder pandemic that seems to have embraced our society. Usually said by people who a) have never read a book, b) have no logical retort, c) want an easy laugh, or any combination of the three. Not to be confused with "TMS;DU", meaning "Too Many Syllables; Don't Understand", which is likely how some of you reading this feel about this definition.

Spanky - "I find it hilarious that any definition of TL;DR condeming those who use it as uneducated morons, are the ones receiving more thumbs down - just like this one probably will - even though they are the most accurate. That just further proves that people - especially kids - have a consistantly dwindling attention span, most likely indirectly proportional to the amount of media and entertainment devices we feel the need to constantly plug ourselves into."
Spunky - "... TL;DR"
Spanky - "Are you sure it wasn't TMS;DU?"
Spunky - "... l0zz0rs, pwned."

A) "Too long; didn't read.", meaning a post, article, or anything with words was too long, and whoever used the phrase didn't read it for that reason.

B) Also used by someone who wrote a large posts/article/whatever to show a brief summary of their post as it might be too long.

a)
Guy One: Did you read that book for English class?

Guy two: No, tl;dr.

B)
Guy one: Cake is a form of food that is usually sweet and often baked. Cakes normally combine some kind of flour, a sweetening agent (commonly sugar), a binding agent (generally egg, though gluten or starch are often used by vegetarians and vegans), fats (usually butter, shortening, or margarine, although a fruit purée such as applesauce is sometimes substituted to avoid using fat), a liquid (milk, water or fruit juice), flavors and some form of leavening agent (such as yeast or baking powder), though many cakes lack these ingredients and instead rely on air bubbles in the dough to expand and cause the cake to rise. Cake is often frosted with buttercream or marzipan, and finished with piped borders and crystallized fruit.1

Cake is often the dessert of choice for meals at ceremonial occasions, particularly weddings, anniversaries and birthdays. There are literally millions of cake recipes (some are bread-like and some rich and elaborate) and many are centuries old. Cake making is no longer a complicated procedure; while at one time considerable labor went into cake making (particularly the whisking of egg foams), baking equipment and directions have been simplified that even the most amateur cook may bake a cake.